1. Field of the Invention
The present invention relates to a system for directly detecting tire inflation pressure and more specifically to a transceiver including a pressure sensor that is directly attached to each of wheels and that transmits a detection signal produced by the pressure sensor to a receiver mounted on a vehicle body in order to detect a tire inflation pressure.
2. Description of the Related Art
In direct type tire inflation pressure detection systems, since a transceiver that sends tire inflation pressure data to a receiver on a vehicle body side is attached to each of wheels, if the transceiver is replaced with another during replacement of a tire, ID information inherent to the transceiver is changed to another. When the receiver receives a radio wave carrying tire inflation pressure data, the ID information is used to decide whether the radio wave is radiated from a subject vehicle or another vehicle. Therefore, when the ID information is changed to another, the new ID information has to be re-registered in the receiver. Methods described in JP-A-2000-71726, Japanese Patent No. 3661670, JP-A-2006-15895, and JP-A-2006-123725 have been proposed for automatically registering such ID information.
To be more specific, according to JP-A-2000-71726, a frequency of reception within a certain period is taken into account. Among multiple elements of data including unknown ID information having been received, elements of unknown ID information that are received frequently are recognized as elements of ID information associated with a subject vehicle, and registered.
According to Japanese Patent No. 3661670, based on data elements concerning the temperatures in tires and tire inflation pressures retrieved from multiple elements of received data including unknown ID information, data including ID information that is carried by a radio wave and contains the temperature in a tire or a tire inflation pressure that correlates to the driving pattern of a subject vehicle is registered as being associated with the subject vehicle. For example, as a subject vehicle continues to be driven, the temperatures in tires or tire inflation pressures increase. If data concerning a temperature in a tire or a tire inflation pressure represents a correlative result when correlated with previous data, the data is recognized as being associated with the subject vehicle and the ID information containing the data is registered.
According to JP-A-2006-15895 and JP-A-2006-123725, when radio waves carrying multiple elements of data including unknown ID information are received, a receiver on a vehicle body side measures the intensities of the received radio waves. Data elements including ID information associated with a subject vehicle are discriminated from data elements including ID information associated with another vehicle on the basis of the intensities, and are then registered.
However, if another vehicle is driven in relatively close proximity to the side of a subject vehicle, the reception of radio waves sent from the other vehicle being driven nearby becomes more frequent. Further data elements associated with the temperatures in tires or tire inflation pressures included in the radio waves of the other vehicle may correlate to the driven state of the subject vehicle. Still further, since the subject vehicle and the other vehicle are located mutually closely, the intensities of the radio waves received from the other vehicle are as large as those associated with the subject vehicle. Therefore, it becomes clear that in a situation where another vehicle is driven in relatively close proximity to the side of a subject vehicle, ID information cannot be accurately registered according to the above described techniques.